At present, the communications spectrum is at a premium, with projected high capacity requirements of Personal Communication Systems (PCS) adding to the problem. Although all modulation techniques for wireless communications suffer capacity limitations due to co-channel interference, spread spectrum, or Code Division Multiple Access (CDMA), is a modulation technique which is particularly suited to take advantage of spatial processing to increase user capacity. Spread spectrum increases signal bandwidth from R (bits/sec) to W (Hz), where W greater than  greater than R, so multiple signals can share the same frequency spectrum. Because they share the same spectrum, all users are considered to be co-channel interferers. Capacity is inversely proportional to interference power, so reducing the interference increases the capacity.
Some rudimentary spatial processing can be used to reduce interference, such as using sector antennas. Instead of using a single omnidirectional antenna, three antennas each with a 120 degree sector can be used to effectively reduce the interference by three, because, on average, each antenna will only be looking at ⅓ of the users. By repeating the communications hardware for each antenna, the capacity is tripled.
Ideally, adaptive antenna arrays can be used to effectively eliminate interference from other users. Assuming infinitesimal beamwidth and perfect tracking, adaptive array processing (AAP) can provide a unique, interference-free channel for each user. This example of space division multiple access (SDMA) allows every user in the system to communicate at the same time using the same frequency channel. Such an AAP SDMA system is impractical, however, because it requires infinitely many antennas and complex signal processing hardware. However, large numbers of antennas and infinitesimal beamwidths are not necessary to realize the practical benefits of SDMA.
SDMA allows more users to communicate at the same time with the same frequency because they are spatially separated. SDMA is directly applicable to a CDMA system. It is also applicable to a time division multiple access (TDMA) system, but to take full advantage of SDMA, this requires monitoring and reassignment of time-slots to allow spatially separated users to share the same time-slot simultaneously. SDMA is also applicable to a frequency division multiple access (FDMA) system, but similarly, to take full advantage of SDMA, this requires monitoring and reassignment of frequency-slots to allow spatially separated users to share the same frequency band at the same time.
In a cellular application, SDMA directly improves frequency re-use (the ability to use the same frequency spectrum in adjoining cells) in all three modulation schemes by reducing co-channel interference between adjacent cells. SDMA can be directly applied to the TDMA and FDMA modulation schemes even without re-assigning time or frequency slots to null co-channel interferers from nearby cells, but the capacity improvement is not as dramatic as if the time and frequency slots are re-assigned to take full advantage of SDMA.
Instead of using a fully adaptive implementation of SDMA, exploitation of information on a users"" position changes the antenna beamforming from an adaptive problem to deterministic one, thereby simplifying processing complexity. Preferably, a beamformer uses a simple beam steering calculation based on position data. Smart antenna beamforming using geo-location significantly increases the capacity of simultaneous users, but without the cost and hardware complexity of an adaptive implementation. In a cellular application of the invention, using an antenna array at the base station (with a beamwidth of 30 degrees for example) yields an order of magnitude improvement in call capacity by reducing interference to and from other mobile units. Using an antenna array at the mobile unit can improve capacity by reducing interference to and from other cells (i.e., improving frequency reuse). For beamforming, the accuracy of the position estimates for each mobile user and update rates necessary to track the mobile users are well within the capabilities of small, inexpensive Global Positioning System (GPS) receivers.
In general, the present invention is a communication system with a plurality of users communicating via a wireless link. A preferred embodiment of the invention is a cellular mobile telephone system. Each user has a transmitter, receiver, an array of antennas separated in space, a device and method to determine its current location, hardware to decode and store other users"" positions, and beamformer hardware. The beamformer uses the stored position information to optimally combine the signals to and from the antennas such that the resulting beam pattern is directed toward desired users and away from undesired users.
An aspect of the invention uses a deterministic direction finding system. That system uses geo-location data to compute an angle of arrival for a wireless signal. In addition, the geo-location data is used to compute a range for the wireless signal. By using the determined angle of arrival and range, a system in accordance with the invention can deterministically modify the wireless signal beam between transceivers.